Harmonic information detection technique

ABSTRACT

An optical tracking system wherein a first control means tends to lock a nutation electron beam upon and within the image of a target which has been projected upon a screen and constitutes a dark body upon a light background. A second control means functions to expand the nutating scanning pattern of the electron beam until it cuts across the light background in at least two different places to generate a signal whose frequency is equal to the second harmonic of the nutating scanning pattern. Said second control means maintains the amplitude of this second harmonic within certain limits to thereby insure that the scanning pattern always remains approximately the same size as the target. Other logic means are provided to cause the nutating scanning pattern to find and lock-on upon the target should the target suddenly reflect the sun and become a bright object upon a dark background.

United States Patent Henderson [451 Aug. 1,1972

[54] HARMONIC INFORMATION DETECTION TECHNIQUE [72] Inventor: Charles R. Henderson, Arlington,

Tex.

[73] Assignee: L'I'V Aerospace Corporation, Dallas Tex.

[22] Filed: Dec. 21, 1970 [2]] Appl. No.: 99,888

[52] US. Cl. ..l78/6.8, 178/DIG. 2l [51] Int. Cl .JlMn 3/32 [58] Field of Search ..178/6.8, DIG. 21

[56] References Cited UNITED STATES PATENTS 3,l 14,859 lZ/I963 Fathauer et al ..l78/DlG. 21

Primary Examiner-Robert L. Griffin Assistant ExaminerRichard K. Eckert, Jr. Att0rneyH. C. Goldwire and James M. Cate '5 V2 NOTATION SIZE CONTROL PULSE INITIATED ALO CONTROL PULSE ENVELOPE ABSTRACT An optical tracking system wherein a first control means tends to lock a nutation electron beam upon and within the image of a target which has been pro jected upon a screen and constitutes a dark body upon a light background. A second control means functions to expand the nutating scanning pattern of the electron beam until it cuts across the light background in at least two different places to generate a signal whose frequency is equal to the second harmonic of the nutating scanning pattern. Said second control means maintains the amplitude of this second harmonic within certain limits to thereby insure that the scanning pattern always remains approximately the same size as the target.

Other logic means are provided to cause the nutating scanning pattern to find and lock-on upon the target should the target suddenly reflect the sun and become a bright object upon a dark background.

8 Claim, 16 Drawlng'Figures STABLE OPERATING CONDITION SECOND HARMONIC LOCK-ON IN EFFECT AUTOMATIC BREAK LOCK (ALOI DISABLE PULSE INITIATEO GENERATED TARGET mo POLARITY PATH SIMPLE LOCK-ON REVERSAL T0 TARGET EFFECTED EFFECTED i MUTATION SIZE CONTROL PULSE TERMINATED AND SECOND HARMONIC LOCKON EFFECTED BREAK LOCK DISABLE PULSE TERMINATE!) PATENTEU B 1 I973 sum 0s m 12 mmmqnm JOKFZOQ 0mm m 0mm m b9; 0mm 0 muzmmmnooo xoo Txdmmm ww o 2952.32

zmioom 0.222%

CHARLES R. HENDERSON INVENTOR PATENTEDAUB I I972 3.681.528

SHEET 08 [1F I2 I+ 0 T L A SIGNAL IN THIS AREA VT eREAK-LocK occuRs B (THRESHOLD) SIGNAL IN THIS AREA NuTATIoN EXPANDS INTEGRATOR ADJUSTS NUTATION SIZE VREF To KEEP SIGNAL LEVEL 0N v Maw? V (REFERENCE) IF SIGNAL IN THIS AREA NuTATIoN sIzE CONTRACTS FIG /0 FROM ouTPuT OF INTEeRAToR RATE 38 209 /2IO /2Il 2I2 2|3 MEMORY AMPLIFIER RECTIFIER (H OUTPUT 208 T6 2 4 INPUT 0F f INTEGRATOR LOSS-LOCK SIGNAL CLOSED WHEN INITIAL LOCK-ON SWITCH IS ACTIVATED TO DISCHARGE CAPACITOR 2I4, THEREBY CLEARING RATE MEMORY CHARLES R. HENDERSON INVENTOR PATENIEDAUB' 1 m2 SHEET 11 0F 12 0.004 ZO xQOJ 2202141 0200mm m owzzzmmhmo U92 6528 H5 29252 63 29252 8. E013 $3 6. 29252 803 I 8. 1?. E85.

CHARLES R. HENDERSON \NVENTOR HARMONIC INFORMATION DETECTION TECHNIQUE This invention relates generally to systems for detecting and tracking moving objects and more particularly to a system for detecting and tracking moving objects by means of a nutating beam.

Many different systems have been developed for detecting and tracking moving objects. Some of these systems employ radar means, others, such as the well known sidewinder air-to-air attack missile, employ heat detecting means, and some employ optical means. One of the systems employing optical means projects the image of the target upon the screen of an image reproducing tube, such as a vidicon tube. Viewing means are provided whereby the operator of the intercepting aircraft is able to view the image of the target. Still other means are provided for generating a nutating electron beam which can be slewed upon the target image by the operator. The radius of nutation is controllable by the operator so that it is smaller than the body of the target, with the target body usually being darker than the background which ordinarily comprises sky and clouds.

The nutating scanning pattern of the electron beam will move freely about on the dark target body. However, as soon as the scanning pattern begins to move outside the target body, and cuts across a portion of the lighter background, a signal is generated which indicates that the scanning pattern has begun to move off the dark target body. More specifically, while on the dark target body the electron abeam will generate a low level signal, which can be comprised of secondary electron emission, but will generate a greater quantity of secondary electron emission and consequently a higher level signal when it impinges upon a light background.

Since the nutating pattern of the electron beam is generated by sine and cosine voltage functions supplied to the vertical and horizontal deflection windings of the electron beam the occurrence of the signal caused by the nutating beam cutting across the light background will bear a definite phase relation with said sine and cosine deflection voltages. Suitable phase comparing means are provided which compare the signal generated by the nutating beam cutting across the light background with the sine and cosine deflection voltages to produce d-c voltage of the appropriate magnitude. These d-c voltages are applied to the said vertical and horizontal deflection coils and are of appropriate magnitude to move the nutating scanning pattern back onto the dark body of the target.

As the intercepting aircraft approaches the target, however, the size of the target image becomes increasingly larger with respect to the size of nutating electron beam so that the scanning pattern will drift along the dark target body to some extreme portion thereof, such as for example, the tip of the tail or if the target has wings, perhaps to the tip of a wing. Since the intercepting missile will be directed to the center of the nutating scanning pattern it is apparent that the system would be much more likely to ensure destruction of the target if the nutating scanning pattern remained centered on a major portion of the target.

Another problem inherent in the foregoing prior art systems arises when the target body becomes brighter than the background, as for example when the rays from the sun reflect off the target towards the intercepting aircraft. Under such conditions the target body becomes brighter than the background and the nutating electron beam is literally forced off the target and onto the darker background where it moves aimlessly about or perhaps finds a dark cloud to lock upon. In either event the system has become ineffective and the target will escape.

it is a primary object of the present invention to provide an optical detecting and tracking system employing a nutating electron beam which is employed to scan a target image, and wherein the size of the scanning pattern changes in accordance with the size of the target image so that said scanning pattern will remain locked upon a major portion of the target image.

It is a second purpose of the invention to provide a means for detecting and tracking a target employing a nutating electron beam which scans the target image and has a scanning pattern of sufiicient size so that it cuts into the light background in at least two separate places, and with the size of said scanning pattern increasing or decreasing as the size of the target image increases or decreases.

It is a third object of the invention to provide a detecting and tracking system employing a nutating electron beam which always scans a major portion of the target body.

A fourth aim of the invention is to provide a detecting and tracking system employing a nutating electron beam whose scanning pattern locks upon a dark target body and which will search for and relock uponv said target image should said target suddenly become a bright object upon a dark background.

A fifth purpose of the invention is a detecting and tracking system employing a nutating electron beam which scans the target image and which is of sufficient size so that it will pass across the light background in at least two separate places; the size of said scanning pattern being maintained by detecting the second harmonic generated by the passage of the scanning pattern between the light and dark areas of the background and the target body.

A sixth object of the invention is the detecting and tracking of a target by means of a nutating electron beam which scans the optically reproduced target image and which is of a sufficient size to cut across at least two separate portions of the light background to thereby produce a signal output having a component whose frequency is equal to the second harmonic of the nutation frequency, and maintaining the magnitude of said second harmonic component above a predetermined value so that the size of said scanning pattern in turn will always be large enough to scan a major portion of the target.

It is a seventh object of the invention to provide a means for detecting and tracking a target employing a nutating electron beam whose size is-automatically adjustable by appropriate control means to always cut across at least two portions of the light background surrounding the dark target, and which is also capable of performing a similar tracking function of a bright target upon a dark background in the event that the target should suddenly become brighter than the background, and further providing appropriate means for remembering the direction and the rate of speed of the target and also the size of the nutating electron beam scanning pattern during that time period in which the system is accommodating itself to track a light target upon a dark background rather than a dark background upon a light background.

An eighth object is the improvement of optical means for detecting and tracking a moving target, generally.

In accordance with the invention there is provided optical means for projecting an image of the target upon a photosensitive screen. Means are provided to generate a nutating electron beam which can be slewed upon the target image by the pilot of the intercepting aircraft and caused to remain locked thereupon by two interdependent control means. The first of these control means comprises means for generating high and low level signals in accordance with whether the electron beam is scanning the dark body of the target or the light background. A phase comparing means is provided to compare the phases of the sine and cosine functions of voltage signals employed to generate the nutating beam with the phases of the signals generated as the electron beam scans over any portion of the light background. Integrating means are responsive to the output of said phase comparing means to generate d-c voltages which are supplied back to the vertical and horizontal deflecting coils to deflect said nutating scanning pattern away from the light background area and back onto the dark body of the target.

The said second control means comprises a filter which detects a signal component generated by the nutating electron beam as it passes between the light and dark areas of background and target and whose frequency is equal to the second harmonic of the nutating frequency. Means are provided to rectify and integrate the said second harmonic component to produce d-c voltage. The said second control means further functions to compare the generated d-c voltage with a reference d-c voltage to produce a third d-c voltage of a polarity and magnitude which will cause the diameter of the nutating scanning pattern to increase or decrease to maintain the desired amplitude of said second harmonic component. Thus the size of the scanning pattern of the nutating electron beam is caused to be large enough to cut at least two separate portions of the light background. Consequently, the said scanning pattern of said nutating beam will very likely scan a major portion of said target rather than some small portion thereof, such as the wing tip or the end of the tail.

The effects of said first control means and said second control means are, to an extent, opposing effects. More specifically the effect of the said first control means is always to tend to move the nutating scanning pattern entirely back onto the dark body of the target, while the effect of the second control means is to expand said nutating scanning pattern until said scanning pattern cuts across two or more segments of the light background, and thereby generate a second harmonic component of a given magnitude, as described above.

In order to satisfy the requirements of both the first control means and the second control means the sum total of all of the d-c voltages generated by the scanning pattern cutting across the light background, and which are supplied back to the horizontal deflection coil,

must be equal to zero. Similarly all of the d-c voltages generated as a result of the electron beam cutting across the light background, and which are supplied back to the vertical deflection coil, must be equal to zero. If all the d-c voltages supplied to the horizontal coil have a sum total of zero and all the d-c voltages supplied back to the vertical coil have a sum total of zero, then the position of the scanning pattern is stablized as far as the said first control means is concerned. The requirements of the second control means are also satisfied since the scanning pattern is of a size whereby it cuts across a sufficient amount of light background to generate the required second harmonic component.

The said second control means comprises a third control means, herein identified as a function control means. The said function control means performs two major functions, the first being to initiate operation of the system, including the initail lock-on of the nutating scanning pattern onto the target and the second being to recapture the target if a break-lock should occur, i.e. if for some reason the scanning pattern is caused to be dislocated from the target, as for example when the target passes through a'cloud, or when the target suddenly becomes a bright object upon a dark background as occurs when it suddenly reflects the sun's image back to the image reproducing means.

In order to initiate operation of the system the function control means utilizes a signal generating means which causes the nutation pattern to assume a very small angular rotation, which function will be referred to herein as nutation caging. Also during the initiation of operation of the system the function control means will energize an automatic-lock-on circuit (ALO circuit) which functions to generate sine and cosine function voltage signals, which initially have relatively large amplitudes and then rapidly degenerate to smaller amplitudes, thereby providing a collapsing spiral path for the caged nutating scanning pattern. The radius of the spiraling scan is much larger and its angular rotation much less, than the radius and angular rate of the nutating scanning pattern.

The second function of the function control means is a result of the occurrence of a break-lock. In the execution of said second function of the function control means will energize the ALO circuit but will not, however, cage the nutating electron beam. Rather the nutating electron beam will be reduced in size to about one-half of the diameter that it had when break-lock occurred. A rate memory means, which is constructed to retain a continuously updated record of the rate and direction of the target, is also energized by said function control means when break-lock occurs. Thus the general direction and rate of the spiral scanning pattern will move in the direction and at the rate of the target as last recorded.

Also, when break-lock occurs, the function control means will invert the sine and cosine function voltages supplied to the horizontal and vertical deflecting coils of the image tube, to thereby cause the scanning pattern to lock onto a bright target on a dark background. The reason for this change in the basic operation of the system is based on the assumption that break-lock occurred because the target suddenly caught the rays of the sun and thereby became a bright object upon a dark background.

During the aforementioned changes in the circuit that are effected when a break-lock occurs, the second control means is, in effect, disabled in that no changes in the circuit are made as a result of the existence or nonexistence of a second harmonic produced by the electron beam as it passes over its scanning pattern. However, after a very short interval of time of sufficient duration to permit the aforementioned changes in the system to occur, the disabling of the second control means is terminated.

It is assumed that while the second control means is disabled the said first control means will have operated to recapture the target with the caged nutating electron beam. Then when the second control means is reenergized the scanning pattern will be caused to gradually increase in size until the requirements of both the first and the second control means are satisfied.

In accordance with a feature of the invention there is provided an automatic lock-on circuit which responds to a break-lock condition to provide a signal to the horizontal and vertical deflection coils of the image reproducing tube and thereby cause the caged nutating electron beam to follow a collapsing spiral scanning pattern. The mathematical expression for these aforementioned signals supplied from the automatic lock-on circuit to the horizontal and vertical deflection coils of the image reproducing tube are approximated by the following expressions:

e mm g Sin X e cos X X Where X is the frequency function of the spiral scan and is much larger than W,,t the nutation frequency function.

In accordance with a second feature of the invention there is provided gating logic which, upon the occurrence of a break-lock condition, will invert the phases of the sine and cosine function voltages supplied to the horizontal and vertical deflection coils to thereby enable said scanning pattern to reassume lock-on upon said target image if the target has suddenly become brighter than its background.

In accordance with a third feature of the invention, logic means is provided to cage the nutating electron beam to a very small angular value during the initial lock-on procedure, and also to cause said nutating beam to follow a collapsing spiral path under the control of the automatic lock-on circuit.

The above mentioned and other objects and features of the invention will become more clearly understood from the following detailed description thereof when read in conjunction with the drawings in which:

FIGS. 1 and 2 together show a functional logic diagram of the overall system;

FIG. 3 shows how FIGS. I and 2 fit together;

FIG. 4 is a diagram of a target with two nutating scanning patterns shown thereon; the smaller pattern being representative of the type scanning pattern that might be produced by the first control means alone, and the larger pattern representative of the type pattern that might be obtained by the cooperation of the entire system including both the first control means and the second control means;

FIG. 5 is a set of waveforms showing the relationship between the sine and cosine function voltages supplied to the deflection coils of the image reproduction tube and the signals produced as a result of the nutating electron beam cutting across one or more segments of the light background, both for scanning pattern results from the operation of the first control means alone. and also the scanning pattern that results from the cooperation of both the first and second control means;

FIG. 6 is a diagram of the logic means by which the sine and cosine function voltages which are supplied to the horizontal and vertical deflecting coils of the image reproducing tube are inverted in the event that the target suddenly becomes brighter than the background;

FIG. 7 is a logic diagram of the function control means of FIG. 1;

FIG. 8 is a set of waveforms of the pulses generated by said function control means of FIG. 7;

FIG. 9 is a combination logic and schematic diagram of the nutation generating and control means of FIG. 1;

FIG. 10 is a chart showing the relation between the d-c value of the rectified second harmonic component generated by the scanning electron beam and the desired size of the scanning pattern;

FIG. 11 is a combination schematic and logic diagram of the rate memory of FIG. 1;

FIG. 12 is a vector diagram illustrating the balanced condition of d-c voltage components supplied to the horizontal and vertical deflection coils of the image reproducing tube when the scanning pattern is stabilized upon a dark target positioned upon a light background;

FIG. 13 is another vector diagram showing the d-c voltage components generated by the electron beam and supplied to the horizontal and vertical deflection coils of the image reproducing tube when the target suddenly becomes a light object upon a dark background;

FIG. 14 is a diagram showing the scanning path of the electron beam as the system passes from a stable operating condition to a break-lock condition, and then back to a stable operating condition;

FIG. 15 is a diagram showing the scanning path of the electron beam during the initial lock-on period;

FIG. 16 is a set of curves showing the amount of second harmonic signal generated.

The description of the invention will be organized in accordance with the following organization outline.

I GENERAL DESCRIPTION OF SYSTEM A LOGIC FOR MAINTAINING NUTA'TING ELECTRON BEAM LOCKED ON TARGET IMAGE (FIGS. 1, 2, 4 and 5) B LOGIC FOR EXPANDING SIZE OF NU'TAT- ING ELECTRON BEAM SUFFICIENTLY TO GENERATE SECOND I'IARMONICSIGNAL (FIGS. 1, 2, 4, 5 and 10) C CONTROL LOGIC FOR REESTABLISI-IING LOCK-ON TO TARGET IMAGE AFTER BREAK- LOCK OCCURS (FIGS. 6, 7, 8, 9 and I l) D CONTROL LOGIC FOR ORIGINALLY IN- ITIATING FINDING OF TARGET IMAGE AND LOCK-ON THEREOF (FIGS. 7, 8, 9 and 10) II DESCRIPTION OF OPERATION OF THE SYSTEM A OPERATION DURING INITIAL START-UP MODE B OPERATION DURING STEADY STATE OPERATING MODE C OPERATION DURING BREAK-LOCK MODE AND RECAP'TURE OF TARGET In describing the invention several phrases will be employed repeatedly to describe various functions of the system. Some of these phrases are defined in a general manner immediately below in order to enable the reader to better understand the following description.

A. Simple lock-on the locking on of the nutating scanning pattern of the electron beam entirely within the body of the target. Each time the scanning pattern attempts to move onto the background a voltage is generated which causes the scanning pattern to move back onto the target B. Harmonic lock-on This condition exists alter simple lock-on has occurred and the nutating scanning pattern has been caused to enlarge in diameter until two or more portions of the background are cut by the scanning pattern to generate a second harmonic output signal whose amplitude is employed to stabilize the size of said nutating scanning pattern. The position of the scanning pattern on the target is also stabilized.

C. Break-lock disable A function whereby if, after harmonic lock-on has occurred, the target should be lost due to its passing behind a cloud or if it should suddenly reflect the sun and become a bright object on a dark background, for example, logic which detects the second harmonic component is, in effect, disconnected from the systems so that a simple lock-on can be initiated.

D. Memory rate A logic means which memorizes the rate and direction of the target image on the image reproducing tube so that the system will know approximately where to search for the target after a break-lock disable has occurred.

E. Automatic lock-on spiral scan A logic means which is energized upon the occurrence of a breaklock disable condition to cause a reduced-insize scanning pattern to follow a collapsing spiral path whose nominal center in turn follows the remembered path of the target.

F. Nutation reduced A logical function whereby,

in preparation to recapture a target after a breakdisable has occurred, the size of the nutation scanning pattern is reduced to approximately half its operating size.

G. Nutation cage A logical function wherein the diameter of the scanning pattern of the nutating electron beam is reduced to a very small value in preparation for establishing a simple lock-on to a target when the system is energized initially.

I. GENERAL DESCRIPTION OF SYSTEM A. LOGIC FOR MAINTAINING NUI'ATING ELEC- TRON BEAM LOCKED ON TARGET IMAGE FIGS. 1, 2, 4 and 5.

The structures of FIG. I and FIG. 2 represent the overall system and must be considered together in accordance with the diagram of FIG. 3. Such overall system can be divided generally into two main control logic means: one of these control logic means included within the dotted block in FIG. I and the other main control logic means comprises the remainder of FIGS. 1 and 2.

It is to be understood that these two main control logic means are not completely independent of each other and, in fact, cooperate with each other to maintain the electron beam nutating scanning pattern at a definite size with respect to the target, and also locked upon said target.

The logic for maintaining simple lock-on of the scanning pattern upon the target is comprised essentially of that logic of FIGS. 1 and 2 lying outside the dotted block 100, whereas the logic lying within the dotted block 100 is employed to enlarge the scanning pattern of the nutating electron beam until it cuts into the light background around the target to generate the desired second harmonic from which the size of said nutating scanning pattern with respect to the target body can be approximated.

Consider first the logic outside the dotted block 100, Le. the logic employed to establish a simple lock-on of the scanning pattern upon the target. The block 29 is divided into three partitions 30, 31 and 32 which represent, respectively, an optical means 30 for projecting an image of the target upon an image reproducing means 31. A scanning means 32 is provided to scan the reproduced image in a nutating scanning pattern.

When the operation of system is initiated originally, it is necessary that the pilot manually slew the nutating scanning pattern upon the target, at which time the start-up logic, which will be described in detail later, will function to search the immediate area at which the nutating beam is directed until it finds the target and simple lock-on will occur.

During simple lock-on the scanning pattern can move freely about the dark body of the target and an output signal will be generated by the scanning means only when the nutating scanning pattern begins to move off the dark body of the target and onto the light background area.

As is well known in the art the nutating scanning pattern is obtained by applying sine and cosine function voltages to the vertical and horizontal deflection coils of the electron beam which is scanning the target image. Should the scanning pattern begin to move off the dark body of the target and onto the light background area the said scanning pattern will cut across that portion of the light background area upon which it has moved during a time period which bears a very specific phase relation with the sine and cosine voltages which are generating the nutating scanning pattern.

The horizontal deflection phase comparator 36 and the vertical deflection phase comparator 42 function generally to compare any signal generated by the movement of the scanning pattern 011' the dark body of the target with the sine and cosine function voltage driving the vertical and horizontal deflection coils.

In order to provide better phase comparison the actual signals supplied to the phase comparators 36 and 42 are square waves rather than sine and cosine waveforms. Specifically such square waveforms are shown as waveforms C and D of FIG. 5 and can be seen to be in phase with the cosine and sine waveforms of curves A and B, insert respectively, of FIG. 5. The

square wave signals of waveforms C and D are identified herein as phase comparator reference signals. The signals represented by waveforms A and B of FIG. 5 are the signals supplied to the horizontal and vertical deflection coils.

Each of the phase comparators 36 and 42 functions in cooperation with integrators 38 and 44 to produce dc voltages which are supplied back to the vertical and horizontal deflection coils 33 and 34 through summers 39 and 45 and amplifiers 40 and 46, and which have a magnitude and a polarity calculated to move the scanning pattern away from any light background which it is intercepting and back into the dark body of the target.

Integrators 38 and 44 and amplifiers 40 and 46 are conventional devices which need no further explanation. The summers 39 and 45 are simply voltage adding circuits which combine the outputs of integrators 38 and 44 with other signals supplied thereto from leads 91' and 92, and also the output from the automatic lock-on circuit 101 to produce other functions which will be described later. In the absence of signals appearing on the leads 91' and 92', and in the absence of an output from the automatic lock-on circuit 101, the only signals passing through the summers 39 and 45 are those d-c voltages appearing at the output of integrators 38 and 44 respectively.

A typical scanning pattern which might be generated by the simple lock-n logic (outside the block 100) might be a pattern as represented by scanning pattern 111 of FIG. 4. The scanning pattern 1 11 is shown as intercepting a small portion 113 of the light background around the target 110. A pulse P (waveform E of FIG. is generated during the time said scanning pattern is cutting across the segment 113 of the light background and a force F is generated which tends to push the scanning pattern 111 downward and to the left, back onto the body of target 1 10.

A typical scanning pattern which will be generated when all of the logic of FIGS. 1 and 2 is employed i.e. both the simple and harmonic lock-on logic, is represented by the circle 116 in FIG. 4, which circle can be seen to intercept the light background over four segments 114, 115, 116 and 117. At each of these interceptions of the light background the electron beam will generate a signal which ultimately will be transformed into a d-c voltage tending to push the scanning pattern 116 back onto the dark target. However, since the harmonic lock-on logic requires that second harmonic is generated only as a result of the scanning pattern cutting the light background, a condition of stability can be reached only when the d-c voltage components generated for and supplied to the horizontal deflection coil of the electron beam total to zero, and the d-c components which are generated for and supplied to the vertical deflection coil of the electron beam also total to zero.

Reference is again made to the waveforms A, B, C, D and E of FIG. 5 which illustrate the signals required to generate the simple lock-on scanning pattern 111, including the waveform of the signal which is fed back to the deflecting coils to force said scanning pattern 111 downward and to the left in FIG. 4 as a result of its cutting across the light background segment 113.

More specifically in FIG. 5 the waveforms A and B show the cosine and sine function voltages which are generated by the signal source in FIG. 1 and which are supplied to the horizontal and vertical deflection coils 33 and 34. The waveforms C and D represent the square wave reference signals which are in phase respectively with the cosine and the sine function voltages of waveforms A and B. The square wave reference signals of waveforms C and D are supplied respectively to the horizontal and vertical deflection phase comparators 36 and 42. The phase relationship between the reference signals supplied to the phase comparators 36 and 42 of FIG. 1 and the cosine and sine function voltages supplied to the horizontal and vertical deflection plates can be seen to be coincident.

Each time the scanning pattern 111 of FIG. 4 cuts the segments 113 of the light background a positive pulse is generated. These positive pulses are shown in the waveform E of FIG. 5 identified as pulses P P, and P for example. It can be seen that each of these pulses P P, and P occurs during the time that both the horizontal and the vertical deflection reference signals of waveform C and D are in their positive half cycles which is in correspondence with the fact that the scanning pattern 111 cuts across the light background segment 113 in the upper right hand quadrant of the circle defined by the scanning pattern 11 l.

The phase comparators 36 and 42 of FIG. 1 then function to pass positive pulses corresponding to the occurrence of the pulses P,, P, and P of waveform E of FIG. 5. These positive pulses are then supplied respectively tointegrators 38 and 44 of FIG. 2, then to summers 39 and 45, and then to the horizontal and vertical deflection signal amplifiers 40 and 46. The resultant d- 0 output voltage from the horizontal and vertical deflection amplifiers 40 and 46 is then supplied back to the horizontal and vertical deflection coils 34 and 33 to push the scanning pattern 111 downward and to the left so that it will tend to scan entirely on the black target surface.

It is to be noted that in order to obtain the proper output voltage polarity it is necessary that the positive voltage signal derived from positive pulses P P and P of waveform E of FIG. 5 have their polarity reversed, that is to say the output of the horizontal and vertical deflection amplifiers 40 and 46 must be a negative d-c voltage. While such polarity inversion can occur anywhere in the circuit the amplifiers 40 and 46 are herein designated as performing the polarity inversion function. I B LOGIC FOR EXPANDING SIZE OF NUTAT- ING ELECTRON BEAM SUFFICIENTLY TO GENERATE SECOND l-IARMONIC SIGNALS (FIGS. 1, 2,4,5 and 10) Once the nutating scanning pattern has obtained simple lock-on upon the dark target it is desirable to expand the scanning pattern until it cuts at least two separate segments of the light background, thereby assuring that the size of the scanning pattern is somewhat proportionate to the size of the target image. More specifically, if the target image is small then the scanning pattern should be small. If the target image is large, the scanning pattern should be large.

As the intercepting aircraft approaches the target and its image size increases, the scanning pattern should also increase. By such increasing of the scanning pattern size random movement of the scanning pattern within the dark body of the target, perhaps to the end of a wing section or to the tip of the tail, is eliminated.

The logic within block 100 functions to enlarge and maintain the size of the scanning pattern so that it does in fact cut across two or more segments of the light background. Essentially, the increasing of the scanning pattern size to a desired size is accomplished by detecting the second harmonic generated when the scanning pattern intercepts said two or more portions of the light background.

The output from the image scanning means 32 is supplied through appropriate amplifier means 35 and then into a harmonic filter and rectifier 79, which can be conventional circuits. More specifically the harmonic filter 79 is designed to detect the second harmonic in the signal generated by the scanning electron beam. Such second harmonic is rectified and supplied to integrator 94 which generates a d-c voltage proportional to the amount of said second harmonic supplied thereto. Such d-c voltage is then supplied to nutation generating and control means 90 which contains a reference voltage V against which the d-c output of generator 94 is compared.

As a result of the comparison of the output of integrator 94 and the reference voltage V,.,,-, the sine and cosine function output voltages appearing on output terminals 91 and 92 are either increased or decreased to increase or decrease the size of the nutating scanning pattern. More specifically the sine and cosine function voltages appearing on output terminals 91 and 92 are supplied back to the vertical and horizontal deflection coils 33 and 34 through the summer circuits 39 and 45 and the amplifiers 40 and 46, respectively. Such sine and cosine function voltages create the nutating scanning pattern with the magnitude, thereof determining the size of such scanning pattern. Assume the scanning pattern grows to the size represented by pattern 112 of FIG. 4.

Referring now to the waveform F of FIG. there is shown the pulses generated by the target image reproducing tube as a result of the large scanning pattern 112 of FIG. 4 cutting across the segments 114, 115, 116, and 117 of the light background.

Four pulses are generated each complete revolution of the nutating beam. For example, pulses P P P and P of waveform F of FIG. 5 represent the pulses generated as the scanning pattern cuts across the segments 114, 115, 116, and 117, respectively, of the light background, as shown in FIG. 4.

Each of these pulses P, through P generates either a positive or a negative d-c voltage component in both the horizontal and vertical deflection coils. For example, the pulse P will generate a negative d-c voltage for both the vertical and horizontal deflection coils in much the same manner as the pulse P, in the waveform B does. The same logic of FIGS. 1 and 2 is employed to generate d-c voltage components from the pulses P to P, as was employed to generate the d-c voltage com ponents from the pulse P The pulse P, components be seen to occur during the negative half cycle of the horizontal deflection reference signal of waveform C of FIG. 5 and during the positive half cycle of the vertical deflection reference signal of waveform D. Consequently a posi tive d-c voltage will be supplied to the horizontal deflection coil, and a negative d-c component will be supplied to the vertical deflection coil. The resultant effect of these two d-c components is to move the scanning pattern 1 12 in the direction of the vector F a in FIG. 4. Similarly the pulse P, in waveform F of FIG. 5 will result in the generation of d-c components which will tend to move the scanning pattern 112 in a direction indicated by the vector F.. The fourth pulse P, will result in d-c components being supplied to the horizontal and vertical deflection coils which will tend to move the scanning pattern 112 in the direction indicated by vector F In order to stabilize the scanning pattern it is necessary that all of the horizontal or X components of the vectors F F F, and F total to a value of zero. Similarly all of the vertical or Y components of the vector F. through F must total to a value of zero.

Reference is made to FIG. 12 which shows a vector diagram of the four force vectors F through F separated into their horizontal and vertical (X and Y) components. From FIG. 12 and the above discussion it can be seen that the following conditions must exist in order for the position of the scanning pattern 112 of FIG. 4 to be stabilized.

It is to be noted that the pulse train shown in waveform F of FIG. 5 is also supplied to the harmonic filter and rectifier circuit 79 of FIG. 1, wherein the second harmonic generated by the nutating scanning pattern is extracted and rectified, and then integrated in integrator 94. As indicated above the magnitude of the d-c voltage resulting from rectification and integration of the second harmonic must approach the reference voltage V of FIG. 10.

The specific logic to accomplish the expansion or contraction of the scanning pattern 112 to generate such a second harmonic is shown in FIG. 9. While, as discussed hereinbefore, the size of the nutating scanning pattern will be caused to assume different values in accordance with different situations such as during start-up and immediately after a break-lock occurs only the size of the scanning pattern during the stable operating conditions will be discussed in the following few paragraphs.

In FIG. 9 the integrator 94' corresponds to integrator 94 of FIG. 1 and is comprised of operational amplifier 199 and a time constant which includes capacitor 181 and resistor 178.

The output from the harmonic filter and rectifier 79 of FIG. 1 is supplied to the input 196 of integrator 94 through gating means 172. The other input 197 of integrator 94' is connected to the desired reference voltage V shown in FIG. 10 through gating means 174. The voltage reference V, is determined by negative battery source connected in series with resistor 176 which has an adjustable tap 177 connected thereto.

The AND gates 172 and 174 are both normally conductive so that both the output signal from the harmonic filter and rectifier 79 of FIG. 1 and also the voltage reference V,,; are supplied respectively to the input leads 196 and 197 of integrator 94'.

Amplifier 182 amplifies the d-c output of integrator 94' and supplies such amplified output to the gate electrode of field effect transistor (FET) 183. The FET 183 functions as an impedance which varies in accordance with the magnitude of the d-c voltage supplied to the gate electrode from amplifier 182.

The nutation input, which is supplied via lead 190 from the output of the signal source 60 of FIG. I, is then attenuated by FET 183 in accordance with the output of amplifier 182.

Such attenuated signal (E sin wt) is then supplied to integrator 198 which forms a signal E cos wt, in quadrature therewith. Thus, on the output terminals 91 and 92 there appear the sine and cosine function voltages employed to drive the vertical and horizontal deflection coils of the image reproducing tubes. Such sine and cosine function voltages appearing on output leads 91 and 92 are supplied to the summing circuits 39 and 45 of FIG. 2.

Referring again to integrator 94' it can be seen that under normal operating conditions, with gates 172 and 174 conductive, the output voltage of integrator 94' will be determined by the setting of tap 177 on resistor 176, which setting determines the value of the voltage reference V Thus the d-c component of the rectified second harmonic derived from the electron beam as it scans the target image is controlled by the value of V More specifically the value of the d-c component derived from said scanning pattern and appearing at input 196 of integrator 94' will substantially be equal to the reference voltage V supplied to input lead 197. The amplitude of the sine and cosine function voltages appearing on output terminals 91 and 92 are either increased or decreased until the two d-c voltages on input leads I96 and 197 are substantially equal.

l C CONTROL LOGIC FOR REESTABLISHING LOCK-ON TO TARGET IMAGE AFTER BREAK- LOCK OCCURS. (FIGS. 1, 2, 6, 7, 8, 9, and 11) Occasionally the target will catch the rays of the sun and reflect them towards the image reproducing tube, and thereby become a bright object upon a dark background. Due to the simple lock-on logic described above in section I A the scanning pattern consequently is caused to be pushed off the target completely and will then wander at random upon the background which has now become the darker of the two areas. Eventually the scanning pattern will perhaps lock upon a dark cloud, if logic were not provided for recapturing the target.

However, such logic is provided and consist essentially of a memory means which remembers the rate and direction of the target. Such logic also performs the function of reversing the phases of the two quadrature phased phase comparator reference signals supplied to phase comparators 36 and 42 of FIG. 1 so that, in effect, the scanning pattern will now be forced off the darker background and towards the lighter body, which presumably is now the target.

To further enhance the possibility of recapturing the target the size of the nutation scanning pattern is reduced to approximately half of the size it was at the time break-lock occurred. In addition, the automatic lock-on (ALO) feature is initiated which functions to cause the center of said reduced nutation scanning pattern to follow the path of a collapsing spiral whose center moves in a path coincident with the rate and direction of the target as remembered by the logic at the time of break-lock.

FIG. 6 shows the logic for reversing the phases of the phase comparator reference signals which are supplied to phase comparators 36 and 42 of FIG. 1.

It is to be understood that the logic of FIG. 6 is, in essence, a switching circuit, and, functions not only to pass the inverted phase reference signals shown in waveforms G and H of FIG. 5 but also to pass the uninverted phase reference signals shown in waveforms C and D of FIG. 5.

The logic of FIG. 6 will be discussed first in a general manner and then the specific means by which switching is effected to selectively pass either the uninverted or the inverted phase comparator reference signals will be discussed.

In FIG. 6 each of the phase comparators 36' and 42' can be seen to consist of a pair of AND gates whose outputs are supplied to a combining circuit. More specifically the horizontal deflection phase comparator 36' is comprised of AND gates I20 and 121, with the output of AND gate 120 being supplied directly to combining circuit 122 and the output of AND gate 121 being supplied to said combining circuit 122 through inverter 124. AND gate 120 passes a positive pulse in response to coincident positive pulses from the electron beam image reproducing tube 29 of FIG. 1 and the phase comparator reference signal from phase shift logic 67'. The AND gate 121 produces a positive output in response to coincident positive output signals from the image reproducing tube and the negative or lower level signals, from the 90 phase shift circuit 67. However, the output of AND gate 121 is inverted by inverter 124 so that the actual signal supplied to combining circuit 122 from AND gate 121 is a series of negative pulses corresponding in time to the cutting of the light background by the scanning pattern. The combiner I22 combines the positive pulses from AND gate and the negative pulses from AND gate 121 and then supplies the combined pulses through a gating network to ingegrator 38 of FIG. 2. The integrator 38 responds to the train of positive and negative pulse supplied thereto to produce a resultant d-c voltage whose polarity and magnitude indicate the direction and the distance the scanning pattern is to be moved along the horizontal axis. As mentioned above when the scanning pattern is stabilized the output of the integrator 38 will be zero volts.

Similarly the AND gates I25 and 126, the inverters 128 and 129 and the combining circuit 127 function to produce a resultant pattern of positive and negative pulses which are supplied to integrator 44 (FIG. 2) through a gating network to produce a d-c voltage whose polarity and magnitude determine the direction and the distance which the scanning pattern should be moved vertically in order to reach a stable condition.

During normal tracking operation before a breaklock occurs the flip-flop 64' is reset so that AND gate 62' is conductive and AND gate 63' is non-conductive. Thus the output from square wave generator 28' is supplied to the phase comparators 36 and 42' in a non-inverted form. However, when a break-lock occurs an appropriate signal is supplied via lead 85 from the control means 82 of FIG. 1 to set flip-flop 64', and thereby 

1. Tracking means constructed to track a moving target and comprising: image reproducing means comprising a screen and constructed to optically project the image of said target and the background thereof upon said screen; said screen responsive to a beam of charged particles to generate electrical signals whose amplitude varies in accordance with the intensity of the light being projected upon said screen; scanning means comprising a beam of charged particles, a vertical deflecting means for deflecting said beam vertically, and a horizontal deflecting means for deflection said beam horizontally; means for supply first signals to said vertical and horizontal deflecting means to cause said beam to describe a nutating scanning pattern at a predetermined nutation rate; starting means for initially causing said nutating scanning pattern to lock-on upon said target image; first control means responsive to the impingement of said beam upon portions of said screen outside said target image to supply to said horizontal and vertical deflecting means signals of a polarity and a magnitude to deflect said beam so that said nutating scanning pattern will tend to remain within said target image when said target image is of a different brightness than said background; second control means responsive to that component of the signal, generated by said beam as it impinges alternately upon said target image and upon portions of said screen outside said target image, whose frequency is equal to a given harmonic of the nutation rate, to cause said nutating scanning pattern to increase in size until said given harmonic signal component reaches a predetermined amplitude.
 2. Tracking means in accordance with claim 1 and further comprising: rate memory means for continuously recording a second signal representative of the direction and velocity of said target image upon said screen; nutation scanning pattern size memory means for continuously recording a third signal representative of the scanning pattern size; and logic control means responsive to the loss of lock-on of said nutating scanning pattern upon said target image to connect the second signal of said rate memory means and the third signal of said nutation scanning pattern size memory means to said vertical and horizontal deflecting means to cause the nominal center of said scanning pattern to follow the remembered path of said target image at the remembered velocity and to regain lock-on of said scanning pattern upon said target image.
 3. Tracking means in accordance with claim 1 and further comprising: rate memory meanS for continuously recording a second signal representative of the direction and velocity of said target image upon said screen; nutation scanning pattern size memory means for continuously recording a third signal representative of the nutation scanning pattern size; automatic lock-on scanning mean constructed to cause the nominal center of the nutating scanning pattern to follow a collapsing spiral pattern; and logic control means responsive to a loss of lock-on of said nutating scanning pattern upon said target image to connect said rate memory means, said nutation scanning pattern size memory means, and said automatic lock-on scanning means to said vertical and horizontal deflecting means to cause the nominal center point of said nutating scanning pattern to follow a path defined by said collapsing spiral pattern with the nominal center of said collapsing spiral being translated along the remembered path of said target image and with the remembered velocity of said target image, and to regain lock-on of said scanning pattern upon said target image.
 4. Tracking means in accordance with claim 2 in which said first control means further comprises: polarity reversing means responsive to loss of lock-on upon said target image by said scanning pattern to condition said first control means to deflect said electron beam so that said nutation scanning pattern tends to remain within said target image with the relative brightnesses of said target image and the portions of said screen surrounding said target being reversed.
 5. Tracking means constructed to track a moving target and comprising: a screen constructed to assume different energy states in response to images optically projected thereon and to be responsive to an impinging electron beam to generate a signal whose amplitude varies in accordance with the energy level of that portion of the screen upon which the electron beam is impinging; means for projecting the image of said target upon said screen; scanning means comprising an electron beam and deflecting means for deflecting said electron beam in vertical and horizontal directions; means for supplying first signals to said deflecting means to cause said electron beam to describe a nutating scanning pattern upon said screen; starting means for initially establishing lock-on of said nutating scanning pattern upon said target image; first control means responsive to the impingment of said electron beam upon a portion of said screen outside said target image to supply a second signal to said deflecting means to deflect said electron beam so that said nutating scanning pattern tends to remain within said target image; and second control means responsive to a signal component of a given frequency which is generated by said electron beam as it scans alternately between portions of the target image and portions of the screen outside said target image, to cause said nutating scanning pattern to increase in size until said signal component reaches a predetermined amplitude.
 6. Tracking means in accordance with claim 5 and further comprising: rate memory means for continuously recording a second signal representative of the direction and velocity of said target image upon said screen; nutation scanning pattern size memory means for continuously recording a third signal representative of the scanning pattern size; and logic control means responsive to the loss of lock-on of said nutating scanning pattern upon said target image to connect the second signal of said rate memory means and the third signal of said nutation scanning pattern size memory means to said electron beam deflecting means to cause the nominal center of said scanning pattern to follow the remembered path of said target image at the remembered velocity and to regain lock-on of said scanning pattern upon said target image.
 7. Tracking means in accordance with claim 5 and further comprising: rate memory means for continuously recording a sEcond signal representative of the direction and velocity of said target image upon said screen; nutation scanning pattern size memory means for continuously recording a third signal representative of the nutating scanning pattern size; automatic lock-on scanning means constructed to cause the nominal center of the nutating scanning pattern to follow a collapsing spiral pattern; and logic control means responsive to a loss of lock-on of said nutating scanning pattern upon said target image to connect said rate memory means, said nutation scanning pattern size memory means and said automatic lock-on scanning means to said electron beam deflecting means to cause the nominal center point of said nutating scanning pattern to follow a path defined by said collapsing spiral pattern with the nominal center of said collapsing spiral being translated along the remembered path of said target image and with the remembered velocity of said target image, and to regain lock-on of said scanning pattern upon said target image.
 8. Tracking means in accordance with claim 7 in which said first control means further comprises: polarity reversing means responsive to loss of lock-on upon said target image by said scanning pattern to condition said first control means to deflect said electron beam so that said nutation scanning pattern tends to remain within said target image with the relative brightnesses of said target image and the portions of said screen surrounding said target image being reversed. 